1. Field of Invention
The invention relates to the reception of electromagnetic waves of high frequency including "Extremely High Frequency" (EHF) waves and to mixers and antennamixer combinations formed in a planar configuration which are suitable for use in antenna arrays at EHF and lower frequencies.
2. Description of Prior Art
The reception of waves at extremely high frequencies has required new fabrication techniques and new topologies. The need has arisen for topologies suitable to the range of frequencies which includes millimeter waves (typically 30 to 300 Gigahertz). However since the mixer conventionally changes the input signal waves to intermediate frequencies of a few Gigahertz, the topology must also be suitable to waves of a few Gigahertz. The most promising approach to high frequency circuit topology has been the extensive resort to planar topologies in which the transmission lines take the form of thin conductors patterned upon an insulating substrate by an automated process. At the higher frequencies, it has been proposed that the substrate itself be of a semiconductor material suited to the monolithic integration of both active and passive elements. Such monolithical assembly is particularly advantageous at the higher frequency ranges in simplifying connections. However it is less practical at the lower frequency ranges where the passive circuitry may require larger insulating substrates than are feasible in a semiconductor material. The "hybrid" format employing discrete active devices, is, accordingly, a practical form of the planar topology, when somewhat larger scaled circuitry is needed for lower frequency operation.
With the advent of interest in these frequencies, attention has been directed to performing the necessary circuit functions in the planar format. An example of an unbalanced transmission line in the planar format is the strip line in which a conductor of finite width is supported between two dielectric layers, spaced between upper and lower ground planes. The microstrip represents a simplification of a strip line in that only a single finite conductor, single ground plane, and a single dielectric layer are employed. A balanced planar line called a "coplanar strip" employs paired conductors patterned on the same substrate surface, and is electrically similar to twin line. An unbalanced line called coplanar line (sometimes referred to as coplanar waveguide) employs three conductors patterned on the same substrate surface comprising a center conductor and two finite width ground planes placed either side. Combinations of these transmission lines give promise of providing essentially all the functions previously achieved in waveguide arrangements including both filtering and balancing to provide mutually isolated ports.